1. Field of the Invention
The present invention relates to collets, and more particularly to collets which can be adjusted to accommodate workpieces of different diameters within a specific range of diameters.
2. Description of the Prior Art
Conventional machine tool collets are adjustable in internal diameter in order to grip and release a workpiece, but the adjustment is such that each collet is only suitable for use with a specific diameter of workpiece which the collet grips along the entire length of its gripping segments. This gripping action can only be achieved with one specific workpiece diameter, and therefore a different collet is required for workpieces of different diameter.
There has been disclosed in U.S. Pat. No. 2,346,706 issued to Stoner, a collet which can be adjusted to accommodate workpieces of diameters within a specific range. In certain embodiments this collet consists of separate segments with rubber plate-like elements interposed between adjacent segments. The faces of the rubber elements are adhered to the opposed radial faces of the adjacent segments or have projections which engage in recesses in the opposed faces of adjacent segments. The segments of the collet can be moved inwardly to clamp different diameters of workpiece, but due to the connection between the rubber elements and the faces of the segments, the rubber elements provide substantial resistance to inwards movement of the segments which, in effect, absorbs much of the closure force applied to the collet by an associated closure mechanism.
U.S. Pat. No. 2,557,301 issued to Lundy discloses a collet with rubber-like inserts between adjacent segments. The inserts have a ribbed construction in one embodiment, with the ribs in contact with the adjacent radial faces of the segments. These inserts act simply as seals. The segments are not separate segments, so that this collet is not adjustable for different workpiece diameters. Similar sealing inserts are disclosed in U.S. Pat. Nos. 3,539,193 and 3,669,462, both issued to Parsons.
British Pat. No. 1,245,418 issued to Fahrion teaches a collet with rubber plate-like inserts located between adjacent segments. Although this collet is disclosed as being adjustable to suit different clamping diameters, the segments are connected at their inner ends and are therefore not capable of displacement parallel to the axis of the collet. Instead, they would tend to pivot inwardly about their inner connected ends and would not be exactly parallel with the workpiece at different clamping diameters. Further, the radial dimensions of the inserts is substantially less than that of the segments, and gaps are left between the radially inner edges of the inserts and the segments. Particles of swarf are liable to enter these gaps, and this may impede correct functioning of the collet.